Apparatus and process for removing oxidation scale from metal

ABSTRACT

The invention provides an improved apparatus and method for removing oxidized and embedded scale from sheet metal by high pressure spraying a diluted hydrochloric acid water mixture onto the surface of the sheet metal. The contaminated water/acid solution is then re-circulated to remove ferrous chloride from the acid and water solution. The cleansed acid and water solution are recycled for reuse. The sheet metal is rinsed with hot water, dried, oiled and rolled. The rinse water is re-circulated to remove acid droplets and the acid droplets are recycled to an acid storage tank. Any contaminants removed from the rinse water are recycled to a combination filter and reverse osmosis system. The clean rinse water is reused to rinse further sheet metal.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an improved apparatus and process for removing oxide scale from processed sheet metal. More particularly, the apparatus and process of the present invention is designed to operate in a self contained environmentally efficient confined space.

BACKGROUND OF THE INVENTION

Sheet metal is commonly manufactured using a hot rolling process. The hot rolling process operates at extremely high temperatures and the finished sheet metal product is usually cooled by running the sheet metal through a water bath. As the sheet metal product is cooled, the surface of the sheet metal reacts with air and forms an iron oxide layer commonly known as scale.

The iron oxide layer on the sheet metal has three distinct layers. A wustite layer is mechanically bonded to the base metal substrate. A layer of magnetite is chemically bonded to the wustite and a layer of a hematite is chemically bonded to the magnetite.

When the sheet metal is processed for final use, the oxide layers must be removed to provide a flat clean sheet metal surface. The most common method of removing oxide from the surface of hot roll sheet metal is a process known as pickling. The sheet metal is pulled through a hydrochloric acid bath which chemically removes the oxide layers. After the scale is removed, the sheet metal is washed, dried and oiled to prevent further oxidation of the sheet metal surface. Common pickling tanks are 45 to 50 feet long and commonly four tanks are required for the pickling and washing and oiling process. Thus, a pickling operation leaves a large footprint in a factory setting. Further, the use of such vast amounts of hydrochloric acid creates environmental and OSHA concerns for the pickling operators. Acid fumes are common.

An alternative to the pickling acid bath is a method for removing scale such as that shown in U.S. Pat. No. 7,156,926. The '926 patent discloses and claims a surface conditioning apparatus such as rotating brushes coming into engagement with the surface of the sheet metal. The rotating conditioning member or brush removes substantially all of the hematite layer and magnetite layer from the surface of the sheet metal. Additionally, a portion but not all of the wustite layer is removed from the surface of the sheet metal.

For many end users the end product of the '926 methodology is perfectly acceptable sheet metal that can be used in many applications. However, there are some applications that it is essential that all of the oxidized and embedded scale be removed from the sheet metal.

Therefore, it is an object of the present invention to provide an apparatus and method for cleaning sheet metal which removes all three layers of oxidation scale from the surface of the metal.

It is further an object of the invention to provide a relatively compact, environmentally friendly method and apparatus for removing oxidation scale from sheet metal.

Yet another object of the invention is to provide a method and apparatus for removing oxidation scale from sheet metal which virtually results in zero discharge of pollutants.

Yet another object of the present invention is to provide for a method and apparatus for removing oxidized scale from sheet metal which can be used in combination with the apparatus of the '926 patent or can be used as a stand alone unit.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for removing oxidized and embedded scale from sheet metal. Optimally the apparatus includes four tanks, two for use as pickling tanks and two for use as rinse tanks. Each tank is approximately 12 feet long.

The pickling tanks include high pressure sprayers which spray a diluted hydrochloric acid/water mixture onto the surface of the sheet metal as the sheet metal is drawn through the tanks. Each pickling tank has a plurality of removable spray headers located above and below the travel path of the sheet metal. The pickling tanks are separated by squeegee rolls to maintain acid concentration in each pickling tank by removing excess acid dilution from the surface of the sheet metal. An acid collection system is in a tank below the spray compartment. The acid and acidic fumes are recycled in a closed loop. The hydrochloric acid is diluted with water and heated to approximately 180° F. The solution cascade rates, acid feed rates and spray head pressure are adjustable to obtain the most efficient use of the hydrochloric acid.

The rinse system provides heated water to help in drying the sheet metal. Each tank contains three removable spray headers above and below the travel path of the sheet metal. The rinse water is heated to a range of 125-145° F. The acidic rinse water over-flow is fed to a buffer tank and metered from the buffer tank to a neutralizer tank and on to an ultra filter system through a reverse osmosis system. The clean water is sent back to the rinse system for reuse. There is no discharge from the rinse process to the sewer.

The entire pickling and rinse apparatus is approximately 44 feet long.

While the principal advantages and features of the present invention have been described above, a more complete and thorough understanding and appreciation of the invention may be obtained by referring to the figures and detailed description of the preferred embodiments which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the pickling sprayer and rinse apparatus of the present invention.

FIG. 2 is a side elevation of the pickling sprayer and rinse apparatus of FIG. 1.

FIG. 3 is a flow schematic showing the closed loop mechanical operating systems for the pickling tanks and the rinse tanks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIG. 1 and FIG. 2, the apparatus of the present invention includes a first acid tank 10, a second acid tank 12, a first rinse tank 14 and a second rinse tank 16, followed by a drying station 18, oiling station 20, shear 22, and recoiler 24. Each acid tank 10, 12 includes a plurality of upper spray headers 11 and lower spray headers 13. Each rinse tank 14, 16 includes a plurality of upper water spray headers 15 and lower water spray headers 17. The tanks are separated by squeegee rollers 26. There are two squeegee rollers 26 located at the end of the processing line proximate the second rinse tank 16, before the drying station 18.

The acid tanks 10, 12 and rinse tanks 14, 16 are enclosed chambers having removable lids 19 to allow access to the interior of each tank. The tanks are constructed from a material impervious to the affects of acid, preferably granite, including cut granite to guide the sheet metal through the tanks. Fume vents 21 are located at the entrance and exit of each tank proximate the squeegee rollers 26. All fumes and gases resulting from the pickling process are collected by the fume vents 21, cycled through the fume header 23 and cleansed by a candle 28 and fume scrubber 30 (FIG. 3), thereby cleansing the fumes to approximately 99.9% clean. The candle 28 operates as a mist eliminator, drawing out any acidic material from the fumes. The fume scrubber 30 washes the air fumes with water via five internal sieve trays.

The drying station 18 incorporates at least three non-heated air knives 25 with blower nozzles 27 positioned above and below the conveyor 29. The blowers force high pressure air across the surface of the sheet material as it travels across the conveyor 29. The sheet material then travels through a tension pad 31. The clean and dry sheet metal is then passed through an electrostatic oiler 20 to apply various oils to a specified mil thickness, shear 22 and rolled up on the recoiler 24.

Referring now to FIG. 3 a schematic of the operational system for the pickling sprayer and rinse apparatus is shown. A raw acid tank 32 receives a supply of hydrochloric acid, from an outside source such as a tanker truck 33. The raw hydrochloric acid is pumped to the acid mixing tank 34 where the acid is diluted with fresh water as well as some recycled waste water from the fume system as will be expounded upon later herein. Preferably the acid is mixed to a solution of about 6% hydrochloric acid. A pH meter 35 is fixed to the acid mixing tank 34 and is programmed to automatically batch the solution.

The raw acid tank 32 and acid mixing tank 34 are each vented to remove gaseous fumes and send the gaseous fumes to a fume scrubber 30 which operates in conjunction with the candle 28 to remove all remnants of hydrochloric acid from the fumes. Clean air is then vented to the atmosphere through the scrubber fan 36. The fume scrubber 30 and candle 28 also receive gaseous vapors and fumes containing hydrochloric acid that have been removed from the acid tanks 10, 12 and rinse tanks 14, 16 by the fume vents 21. The hydrochloric gaseous fumes are sent through the fume header 23 to the fume scrubber 30 and candle 28 for cleansing. Residual waste acid pulled by the fume scrubber 30 and candle 28 is recycled to the acid mixing tank 34. Thus, there is no discharge of hydrochloric acid or fumes into the atmosphere. Only clean air is vented to the atmosphere.

After the proper acid solution has been attained in the acid mixing tank 34, the diluted acid is pumped at a desired flow rate intended to maintain good pickling and strip line speed to the second acid tank 12. After the second acid tank 12 is filled to an appropriate level, the diluted acid is pumped from the acid tank 12 through a heat exchanger 37 wherein the acid solution is heated to 180° F. and sent to the acid spray headers 11, 13 located in the second acid tank 12. The pumps 51 for the spray header 11, 13 are preferably vector drive motors that can vary the delivery pressure of the acid solution.

After spraying the sheet metal in the second acid tank 12, the water/acid solution becomes slightly diluted. The second acid tank 12 is engaged with the first acid tank 10 to allow the water/acid solution to cascade from the second acid tank 12 to the first acid tank 10. Thus the first acid tank 10 receives a slightly diluted water/acid solution. Again the acid solution is pumped through a heat exchanger 38 and sent to the upper and lower spray headers 11, 13 of the first acid tank 10. Thus, the first acid tank 10 acts as a pre-pickler with an acidic solution of approximately 3% and the second acid tank 12 acts as the heavy pickier using an acid solution of approximately 6%. PH meters 39 are attached to the first acid tank 10 and the second acid tank 12 to monitor the acid solution. When necessary, for instance if the solution in the second acid tank 12 becomes to diluted, the system automatically increases the flow rate of fresh acid solution from the acid mixing tank 34 to the second acid tank 12.

Diluted acid containing waste product consisting mainly of ferrous chloride is removed from the first acid tank 10 and pumped to a ferrous chloride storage tank 39. The ferrous chloride is then pumped to a truck and hauled to a processing facility for treatment to make a new chemical product. The ferrous chloride storage tank 39 is vented to the fume scrubber 30 and candle 28. Any hydrochloric acid contained in the scrubber water produced by the fume scrubber 30 is returned by pump to the acid mixing tank 34.

The heat exchangers 37 receive 50 psig steam that is heated in boiler 40. Condensate removed from the heat exchangers 37 is returned to the boiler feed water tank 41 through condensate return 42. Fumes from the condensate return are vented to the fume scrubber 30 for cleansing.

For the rinse operation, neutralized and filtered water is stored in a reverse osmosis feed tank 43, sent pumped through a reverse osmosis filter 44 and then sent to a rinse surge tank 45 where it is mixed with fresh make-up water. The water is then pumped to the second rinse tank 16 at a programmed flow rate to fit the desired pH and strip line speed. The water is pumped from the second rinse tank 16 through a heat exchanger 45 to the water spray headers 15, 17 of the second rinse tank 16. the rinse water is heated to a range of 125-145° F. Again the pumps 51 are preferably vector drive motors that can vary the delivery velocity of the liquid to the spray headers 15, 17.

The second rinse tank 16 is engaged with the first rinse tank 14 so that water cascades from the second rinse tank 16 into the first rinse tank 14. The water is then again pumped from the first rinse tank 14 to the upper and lower spray headers 15, 17. Fumes collected from the atmosphere of the first and second rinse tanks 14, 16 are collected by the fume vents 21 and sent via the fume header 23 to the candle 28 and fume scrubber 30. Any acid and water collected from the fume scrubber 30 is recycled to the acid mixing tank 34. The rinse water with any residue, such as bits of iron, scale acid and miscellaneous debris resulting from the rinsing of the acid from the sheet metal, flows to a buffer tank 46. The solution is continuously re-mixed and pre-neutralized using a caustic agent such as sodium hydroxide, to correct the pH. The solution is pumped at a steady rate to neutralizer 47 where it is neutralized to maintain a final desired pH of 7.2. The caustic tank 48 stores the caustic agent used to maintain the pH. The rinse water is transferred from the neutralizer 47 to the processor tank 49, where the solids settle out of the solution via a flocculation process, and on to the ultra filter 50. The ultra filter 50 is responsible for removing the solids from the water solution. The solids or sludge is transferred to a filter press 39 for water removal. The cleansed water is then pumped to the reverse osmosis tank 43 for removal of any sodium chloride (TDS) that might be present in the rinse water.

It can be appreciated that the pickling sprayer apparatus of the present invention is an environmentally self-contained unit. All acid travels in a self-contained loop and is constantly recycled. The only discharge from the acid loop is the ferrous chloride which, in itself, is a valuable commodity. The steam lines operate in a self-contained loop. The rinse water system operates in a self-contained loop. No chemical concentrate is released to he atmosphere or sewers. The air cleaning system is completely self-contained and operates in a loop. The only release to atmosphere is clean air.

The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims. 

1. An apparatus for removing oxidized and embedded scale from the surfaces of sheet metal comprising in combination: at least one pickling tank defining a travel path for a sheet metal strip to pass therethrough; a plurality of upper spray headers positioned within the at least one pickling tank and located above the travel path of the sheet metal and a plurality of lower spray headers positioned within the at least one pickling tank and located below the travel path of the sheet metal wherein, the upper and lower spray headers spray an acid solution onto the surfaces of the sheet metal; at least one rinse tank defining a travel path within the tank for the strip of sheet metal; a plurality of upper water spray headers positioned within the at least one rinse tank above the defined travel path and a plurality of lower water spray headers positioned within the at least one pickling tank below the defined travel path; a drying station for receiving rinsed sheet metal from the at least one rinse tank and drying the sheet metal of all rinse solution; a coating station for applying a coating intended to prevent further oxidation of the sheet metal; and a transport station for preparing the coated sheet metal for transport.
 2. The apparatus of claim 1 wherein the coating station is an oiling machine for applying oil to the surface of the sheet metal.
 3. The apparatus of claim 1 wherein the transport station includes a recoiling machine for coiling the sheet metal into tightly wound coils for transport.
 4. The apparatus of claim 1 further including a plurality of squeegee rollers, each of the plurality of squeegee rollers being located proximate each end of the at least one acid tank and each end of the at least one rinse tank.
 5. The apparatus of claim 4 wherein at least two squeegee rollers are positioned between the rinse tank and the drying station.
 6. The apparatus of claim 1 further including a fume collection apparatus for capturing all fumes and gases within the atmosphere of the at least one acid tank and the at least one rinse tank, the fume collection apparatus including a device for removing all contaminants from the collected fumes and gases.
 7. The apparatus of claim 6 further including a candle unit for removing acid mist from the collected fumes and gases.
 8. The apparatus of claim 7 further including a fume scrubber for removing all remaining contaminants from the fumes and gases.
 9. The apparatus of claim 1 further including a raw acid tank for receiving raw acid material from an outside source and an acid mixing tank in connection with the raw acid tank for receiving raw acid from the raw acid tank and acid waste from the fume collection apparatus and water to blend the acid solution to a predetermined concentration.
 10. The apparatus of claim 9 further including pumping means engaged with the acid mixing tank for supplying diluted acid solution to the at least one acid tank, wherein the diluted acid solution is passed through a heat exchanger to be heated and pumped to the spray headers for spraying.
 11. The apparatus of claim 10 further including a contaminant tank wherein contaminated acid solution is pumped from the acid tank to the contaminant tank wherein the acid and water solution is separated from contaminants and returned to the raw acid tank.
 12. The apparatus of claim 11 wherein the raw acid tank, the acid mixing tank, and the contaminant tank are vented to capture all fumes and gases, wherein the vents are engaged with the candle and fume scrubber and the fumes and gases are cleaned by the fume scrubber and candle.
 13. The apparatus of claim 1 further including a reverse osmosis feed tank for receiving filtered fresh water; a reverse osmosis filter and a means for pumping the cleansed water to the rinse surge tank.
 14. The apparatus of claim 13 further including a pump and a heat exchanger wherein the rinse water is heated in the heat exchanger and pumped to the spray headers for hot rinsing the sheet material.
 15. The apparatus of claim 14 further including a buffer collection tank, neutralizer and ultra filter wherein the contaminated water is pumped from the rinse tank overflow to the buffer collection tank, neutralizer and ultra filter for Ph correction and cleansing.
 16. A process for removing oxidized scale from the surfaces of sheet metal comprising the steps of: spraying the surfaces of the sheet metal with a diluted acidic solution; rinsing the surfaces of the sheet metal with water; drying the surfaces of the sheet metal; coating the surfaces of the sheet metal for prevention of further oxidation of the sheet metal; and preparing the coated sheet metal for transport.
 17. The process of claim 16 further including the step of collecting all fumes and gases resulting from the acid spraying step and the water rinsing step and processing the fumes and gases to remove all contaminants.
 18. The process of claim 16 further including the step of collecting all acid sprayed on the surfaces of the sheet metal and processing the collected acid to remove all contaminants from the sheet metal and recirculating the processed acid for reuse.
 19. The process of claim 16 further including the step of collecting all rinse water, acid and contaminants from the surface of the sheet metal, cleansing the contaminants from the acid and water, recycling the acid for reuse in the acid sprayer and recycling the water for reuse in the rinse sprayer. 